[leetcode] 201. Bitwise AND of Numbers Range

题目

Given two integers left and right that represent the range [left, right], return the bitwise AND of all numbers in this range, inclusive.

Example 1:

Input: left = 5, right = 7
Output: 4

Example 2:

Input: left = 0, right = 0
Output: 0

Example 3:

Input: left = 1, right = 2147483647
Output: 0

Constraints:

• 0 <= left <= right <= 231 - 1

思路

从left到right的过程，同时也是数字右侧的0/1不断变动的过程，left到right间所有数字按位与的过程中只有靠左侧位是没有变化的，因此求出两个数字中从左到右的共同位，这些共同位表示的数字就是结果。

代码

python版本：

class Solution:
    def rangeBitwiseAnd(self, left: int, right: int) -> int:
        i = 0
        while left != right:
            left >>= 1
            right >>= 1
            i += 1
        return right << i